The present invention relates in general to a method of and apparatus for measuring and recording the drop height of a container in transit, and more particularly to a method of and apparatus for measuring and recording the drop height of a container in transit by detecting pressure differentials resulting from dynamic elevational changes.
In the design of a protective package for a product, the magnitude of various hazards to which the packaged product may be subjected are determined. Shocks and impacts resulting from accidental free fall drops are hazards to which a package product is subjected. Therefore, it is desirable in the design of protective packages for goods to measure and record the free fall drop to which a packaged product may be subjected.
An R-S Two-Way Ride Recorder sold by Impact Register Company of Champaign, Ill., records simultaneously longitudinal and vertical impact on a chart. The vertical chart readings indicate the acceleration to which crating and merchandise are subjected when tested on vibration tables. The vertical acceleration is related to a mass suspended by a spring. An acceleration in mass in excess of a predetermined value dislodges the mass from a stop.
B & K Instruments, Inc. has sold a Bump Recorder, type 2503, which gives a digital reading of the level of mechanical shock to a package. The apparatus includes a triaxial acceleration sensitive device for monitoring impact in three mutually perpendicular directions. The shock or impact on a package is measured by the acceleration-tremor activity. The velocity level of a bump event is obtained by integrating the acceleration pulse which has exceeded a preset threshold.
Impact-0-Graph of Bedford, Ohio, has sold a Protect-0-Pak shock indicator for determining whether a device has been subjected to excess forces in transit. It is an accelerometer that is sensitive to forces applied from various directions. The apparatus comprises spring-loaded steel balls. The springs are calibrated to a preset value. A shock or impact in excess of the preset value triggers a measuring device.
The apparatus heretofore employed for measuring the impact or shock on packaged goods in transit indicate acceleration. Acceleration is dependent on various factors in addition to drop height, such as angle of impact, characteristic of the impacting surface and the cushioning material surrounding the measuring instrument. Mechanical devices of this type suffer from a lack of acceptable accuracy and from a dependence upon not only the amplitude, but also the duration of the impact shock pulse. Electronic apparatus of this type, while capable of reasonable accuracy in measuring acceleration, are not capable of operating over extended periods of time.
The Yoshino, et al. U.S. Pat. No. 4,302,973, issued on Dec. 1, 1981, for Altitude Difference Measuring Apparatus, discloses apparatus for detecting the difference in altitude between two places by measuring the barometric differential at the two places. At one place, ambient air is hermetically contained in an air pressure holding section. At the other place, the barometric difference between the air pressure in the air pressure holding section and the ambient air pressure is detected to produce electrical signals representative of the difference in altitude between the two places. A semicondutor pressure sensor produces the electrical signal corresponding to the difference between atmospheric pressure at the two places. The semiconductor pressure sensor hermetically seals the air pressure holding section and produces the electrical signal corresponding to the difference in pressures between the chamber of the air pressure holding section and the atmosphere at the location of the second place. A timing circuit controls the start and end of the measurements.
The Hitt, et al. U.S. Pat. No. 4,507,962, issued pn Apr. 2, 1985, for Digital Barometric Altimeter, discloses a digital altimeter for aircraft. The altimeter includes two pressure transducers. One pressure transducer is at the open end of a Pitot tube and the other transducer is at the open end of another tube. A temperature sensor is disposed adjacent each pressure transducer respectively. The two transducers are bridged together and are temperature compensated for balancing the output thereof for accurate pressure reading. A processor receives the balanced, compensated output of the transducers for displaying the altitude.
The Hynecek, et al. U.S. Pat. No. 4,023,562, issued on May 17, 1977, for miniature Pressure Transducer For Medical Use And Assembly Method, discloses a transducer for monitoring fluid pressure within a human body. Semiconductor strain gauge elements are formed on the surface of the silicon diaphragm area of a crystal silicon base. The strain gauge elements are contained in an evacuated fluid-tight chamber. Electrical conductors extend from the chamber to a remote display. The diaphragm is deformed by pressure differential between the sealed pressure reference chamber and fluid external to the implanted pressure chamber.